> Question: This seems to be simply an RF choke on the shield of the coax =
> (same as winding the coax into a loop).....therefore, would it not =
> accomplish the same thing to just wind a high impedance RF choke on a =
> toroid and insert it at the feedpoint between the coax shield and the =
> antenna?
When the frequency is somewhat low it is almost always more
cost effective to use a toroid rather than a string of
beads...assuming the target is a high impedance.
That's because impedance increases by the square of the turns in
a multiturn choke and only at a direct proportional rate with length
of the choke for beads.
As a secondary benefit capacitance across the "choke" increases
the effective impedance, unless frequency is well above the point of
parallel resonance.
One thing you have to watch for is making sure the common mode
impedance at the point where the choke is installed is not highly
capacitive. If the impedance is capacitive the choke can make
things worse. The best thing to do with most antennas is use an
isolated primary and secondary and ground the feedline to a
separate ground a short distance from the feedpoint. Then, after
that point (towards the house) you can add a choke and be sure it
is effective.
73, Tom W8JI
W8JI@contesting.com
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